Able to render themselves invisible, immortal Stealth Guardians like Aiden have been protecting humans from the dark power of the Demons of Fear for centuries. But the demons might soon have a powerful tool in their hands to seduce humans to the dark side. The person to provide them with this elixir is the human scientist Leila. Unbeknownst to her, the drug she's developing to cure Alzheimer's Disease has the unexpected side effect of weakening the mind's resistance to the influence of demons.

As Aiden accepts the assignment to protect Leila, forbidden desire flares between them, and they are forced to rely on the only people they can trust: each other. But even if he can save her from the demons, a union between them might be the most dangerous undertaking of all.